1. Field of the Invention
The present invention relates to an organic electroluminescence device and a method of manufacturing an organic electroluminescence device, and more particularly to an organic electroluminescence device using an Mg—Ag layer as a cathode electrode (“cathode”) and a method of manufacturing the organic electroluminescence device.
2. Discussion of the Background
Generally, an organic electroluminescence device includes organic light-emitting layers between an anode electrode (“anode”) and a cathode. Applying a voltage between an anode and a cathode injects holes and electrons into the organic light-emitting layer from the anode and the cathode, respectively. The holes and the electrons recombine in the organic light-emitting layer to generate excitons, which emit light when transitioning from an excited state to a ground state.
The cathode electrode may have a low work function so that it may easily inject electrons into the organic light-emitting layer. For example, magnesium, which has a work function of 3.46 eV, can be used to form the cathode. However, magnesium may react with external oxygen or moisture, making it difficult to implement a stable organic electroluminescence device.
U.S. Pat. No. 4,885,211 discloses an organic electroluminescence device with a cathode including a magnesium—silver (Mg—Ag) alloy to solve the above-mentioned problem. As a result, an organic electroluminescence device having a long lifespan can be obtained. However, since the cathode may comprise Mg having a thickness of 2,000 Å and Ag having a thickness of 250 Å or less, its overall thickness may deteriorate light transmittance. Therefore, such a structure may not be applied to a top-emission light-emitting structure, but only to a bottom-emission light-emitting structure.
In order to solve such a restriction, U.S. Pat. Nos. 6,030,700, 6,075,316, 6,548,956, and 6,596,134 disclose a cathode including a thin Mg—Ag layer and a transparent conductive oxide (TCO) layer made of ITO, IZO, etc. is formed on the Mg—Ag layer to reduce the cathode's resistance. However, in the above-mentioned patents, when the Mg—Ag layer is 100 Å or less thick, the cathode is formed in a shape of an island, and when the Mg—Ag layer is greater than 200 Å thick, the light transmittance deteriorates. Therefore, it may not be feasible to use such organic electroluminescence devices in a top-emission light-emitting structure. Additionally, the TCO layer is formed on the cathode. Accordingly, when the TCO layer is formed using a sputtering method, dark spots 1 and leakage current 2 may be generated due to sputter damage, as shown in FIG. 1 and FIG. 2.